Download Chapter 18 Earthquakes and Volcanoes

Chapter 18 Earthquakes and Volcanoes
Earthquakes
Review: Cross-section of earth
Our Earth is made up of three majour parts:
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The atmosphere – the gaseous portion.
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The aquasphere – the liquid portion (essentially, the oceans)
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The lithosphere – the solid portion (well, not exactly)
The lithosphere is composed of four layers.
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At the center of the Earth is the inner core. The inner core, even though
it is at 6,000oC is mostly solid iron and nickel. Under normal conditions this
would be liquid but because of the pressure caused by the weight of the
overlying rock, the core remains solid.
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On top of this is the outer core, composed mostly of liquid iron and nickel.
Temperatures here are near 3,000oC.
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Over this is the mantle, a thick layer of magma (a mix of liquid and solid
rock) which is heated near the core and rises to the surface where it cools
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somewhat and sinks toward the center again. This rise and fall is called a
convection current.
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Floating on this sea of magma is a thin (between 5 and 50 km thick) outer
layer of soil, and rock called the crust. Each of the first three layers are
essentially continuous pieces; the crust however is broken up into large
chunks called tectonic plates. The convection currents exert huge forces
on the plates causing them to occasionally move very slightly. When this
happens an earthquake occurs. It is believed that a long time ago, all of
the Earth’s continents formed one large super-continent which has been
named Pangea. This movement over long periods of time has resulted in
the continents being spread apart. This continental movement is referred
to as continental drift.
Because the crust under the oceans is so thin (~5
km) there are many cracks and faults here. The thickness of the crust on land
can be very thick (up to 50 km thick, so there aren’t as many faults here.
Note how most of the majour faultlines are in the oceans!
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A close-up view of a section of crust helps explain how earthquakes and
volcanoes are related to tectonic theory. Places where tectonic plates run into
each other are called converging (or collision) boundaries. Where plates
separate from each other, these boundaries are called diverging (or rifting)
boundaries. Volcanoes can easily form at rifting boundaries, but can also form
near collision boundaries. Earthquakes occur at both types of boundaries. At
collision boundaries huge pressures are constantly driving the plates together;
only once in a while do they ‘slip’ and cause a quake. At rifting boundaries, the
huge upward pressure of magma can send shockwaves as plates are pushed
apart.
Pages 364 and 365 of the student text list 21 majour earthquakes (over the past
400 years) and 22 active volcanoes. Comparing this data to the above map
shows how the two are related. How so?
Generally, evolutionists point to three pieces of evidence to support their
hypothesis of Pangea and continental drift.
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Common animal species in Africa and South America…migration prior to
separation
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Modern continents can be “loosely” fit together like a puzzle…verrrry
loosely.
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Existence of the Mid-Atlantic Ridge…indicates separation on that side of
the world and implies collision in the Pacific area.
Effects of Quakes
On land, ground waves can
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Destroy building structures and bridges
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Destroy underground water supply
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Destroy underground sewer pipes
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Destroy underground natural gas lines
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Knock over electrical transmission lines.
Not only can life be lost in the rubble of toppled structures, but secondary
disasters like explosions and disease often cause more deaths than the
structures do.
At sea, tsunami’s up to 15 stories high can be created when there is a sudden
shift in the sea floor, causing great damage to coastal areas.
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Volcanoes
How their made:
1. Magma from deep in the earth is pushed upward and collects in a large
area called a reservoir.
2. Cracks form in the crust above the reservoir.
3. Pressurized magma forces its way through large cracks (vents)
Typically volcanoes are produced in three locations:
• rifting boundaries – as plates move apart, pressurized magma
breaks through.
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collision boundaries – as over-riding slab is pushed toward
subduction plate, it can buckle and break causing new mountain
formation and huge cracks which allow pressurized magma to push
through.
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hot spots – these are areas away from faults where underlying
magma is hotter than normal. An example of this is the Hawaiian
islands which were formed by this method.
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Effects of Volcanoes
Ash
Explosive eruptions occur when thick magma acts like a corke and ‘bottles up’
gases building up pressures until it simply blows! With the explosion, huge
amounts of ash are discharged. If enough ash is discharged, it will travel great
distances in the upper atmosphere and can affect weather for the next couple of
years.
Ash can also completely bury a location (as was the case with Pompeii in 79 AD
when Mount Vesuvius blew).
Mount St. Helen’s, Washington State
Lava flow
Lava can move slow enough that it gives people enough time to get out of the
way before it destroys everything in its path. Occasionally, like in an explosive
eruption, large amounts of lava can be discharged very quickly.
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Benefits of volcanic activity
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Minerals for plant growth
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Tourism
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New land forms – e.g. Hawaii!
Hikers on the slopes!
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